Peregrine falcons have their share of claims to fame. With a diving speed of over two hundred miles per hour, these birds of prey are the fastest animals on earth or in the sky, and they are now well known for adapting from life on rocky cliffs to a different kind of mountain: modern skyscrapers. But adaptability only helps so much. In 1951, there were no peregrines left in Illinois, for instance, and it looked as if the species would be wiped out entirely in North America. Today, however, peregrines are flourishing.